Investigations undertaken during the past several years identified optimal subsystem designs for a stationary ring, small animal positron emission tomographic (PET) scanner with depth-of-interaction capability. These designs were acted upon during this reporting period, and components for this system were fabricated and procured. All 18 LGSO/GSO "phoswich" detector modules that will surround the animal were assembled and tested. Two three-module sectors were mounted on the gantry ring in opposition to one another and connected to in-house?designed signal-conditioning PC boards containing the module HV supplies and other support electronics. Signal lines emanating from these boards were connected to the data acquisition system that will actually be used in the final device. Initial measurements made with this partial ring suggest that the final system will exhibit a coincidence sensitivity much greater than any existing small animal scanner. Progress was also made toward completing the mechanical assembly of the system. Motors, drivers, power supplies, and screw-driven slides that will wobble the gantry and move the animal bed in all three dimensions were procured and tested, and plans for the layout of these components were formalized. It is expected that physical assembly of the system will be completed by the end of this reporting period and that the first images will be obtained by year's end. In addition to these activities, efforts were begun to procure a small animal computer tomography (CT) scanner to use in conjunction with this PET scanner. CT images of an animal obtained immediately before or after a PET imaging session will be used to correct the PET images for radiation attenuation and other degrading effects and to aid in identification of radiolabeled structures.